I need help to figure out this schematic

Thread Starter


Joined Oct 17, 2011
Hi, following is a part of schematic (please see attachment). 555 is a delay off timer. When power is supplied to timer it energizes the Relay for 10 seconds. Timer itself and other parts are working fine. Yellow 9V supply line is always available to circuit. Red supply line is occasionally available. The goal was to “turn OFF the timer circuit when the RED supply is present and vice versa”. But here PNP transistor is not working properly. I thought it would cut off the timer’s power; when RED supply is present by turning its base high but it is not working as it was supposed to work. Probably I’ve selected the wrong values of biasing resisters. I’ve tried different values of base resisters. Sorry, I’m not expert of electronics and always need suggestions. Some body please trace out the fault. Where I am going wrong? Thanks and regards.